Casings for stuffed products allow a high degree of specialization in relation with the intended applications. Said specialization combines various properties (mechanical properties, gas and/or liquid barrier/permeability properties, cling properties, biological properties, organoleptic properties, etc.) concerning the successive processes and uses to which the casing will be subjected throughout its journey in the market, from the meat industry where it is stuffed to the end consumer. All the properties of a casing render it with a predetermined function in each of the steps of said journey.
A particular combination of properties depends in turn on the material composition and the construction structure of the casing, on the physicochemical treatments to which the casing has been subjected during manufacture, as well as on the incorporation of secondary elements which provide additional properties or modulate the existing ones. These elements generally consist of coatings for coating the inner and/or outer walls of the casing made with substances or compositions different from those of the material making up same.
One of the specializations to which the coatings are intended and which is the object of the present invention is the specialization which emphasizes the cling capacity exerted by some artificial casings on the meat surface which they wrap. When a stuffed product must be subjected to subsequent cooking and/or air curing processes, it is very convenient that the casing does not separate from the meat, since the formation of fat or gelatin bags (in the case of a cooking process) or the formation of air bags as the meat contracts during drying is thus prevented, since in addition to being unsightly they can enhance unwanted fungal growth. It is also important to prevent the skin from separating from the meat when the stuffed product is sliced for consumption.
Until now, coatings used for improving the cellulose casing cling to meat are formed by compositions involving soluble proteins, alone or in combination with acetylated monoglycerides, or chemically modified proteins, in the compositions of which there may or may not be included aldehyde crosslinkers or other carbonyl rich compounds such as liquid smoke. Other substances which provide clinging are chitosan, polyvinyl acetates and some co-polymers thereof and heat curable (also known as thermosetting) polycationic resins; the technique has identified polycationic resins as one of the more effective substances.
Once applied in liquid state, the heat curable polycationic resins used in tubular food films as a surface coating must be subjected to a heating period to harden them and fix them to the surface. This hardening is due to the crosslinking processes resulting from heat-activated intermolecular chemical binding reactions. The polyamino-polyamide-epichlorohydrin resins (epichlorohydrin, epifluorohydrin, epibromohydrin and epiiodohidrin) contain active functional groups reacting with the amine, hydroxyl, carboxyl and thiol groups when heated.
The amounts of resin commonly applied as a coating on the inner surface of the casings are of the order of 0.4 mg/dm2 to 4.8 mg/dm2 (US2010003376A1).
Some classes of casing, for example, reinforced (fibrous) or non-reinforced cellulose casing have, once its production ends, a solid inner coating of cured resin which is anchored to the surface of the casing by means of the same heat curing process of the resin (U.S. Pat. No. 3,378,379). In other words, the cellulose-resin interphase is bridged by chemical bonds while at the same time the resinous phase is entirely crosslinked acquiring a great inner cohesion.
The resin coating acts as a link between the cellulose, to which it is anchored in the curing or crosslinking step, and the meat, to which it clings after stuffing. Even in those occasions in which the resinous cling coating incorporates other substances with cling modulating effect or agents favoring easy peeling (WO 2005/092108 A1), the resin must always be fixed to the casing.
The common method for applying inner cling coating has been determined by the resin curing process. Since the process for manufacturing a cellulose casing always involves a step of drying by means of high temperature hot air, the application of a liquid coating of heat curable polycationic resin is commonly performed in the step before drying, in order to take advantage of:                a) the heat from the drying to start resin curing;        b) the reduction of casing moisture to levels less than 10% to favor the reaction of the resin with the casing and        c) the cellulose tube inflation with air which takes place as it passes through the dryer, since the resin thus creates a cured single-layer of coating which will not stick (blocking effect) to itself when the casing is collapsed again before winding into reels.        
However, this has a serious drawback since the common method for applying inner coatings known in the field as “the bubble” or “slugging” (U.S. Pat. Nos. 3,158,488 or 3,378,379) requires periodically breaking the casing and therefore the process continuity in order to replace the consumed resin in the bubble. Said action is associated with the corresponding economical cost in terms of space, equipment, manpower and efficiency.
In fact, in this “bubble” method:    a) an incision or a cut is made on the casing to enable accessing its interior.    b) a specific volume of coating solution is added into the casing through the opening made. The volume cannot be too large and cause too big a bubble because it becomes unmanageable.    c) the cut ends of the casing are connected again, for example, by means of rubber tubes to restore casing continuity again.    d) the casing is passed between a pair of rollers, such that a layer (“coating”) having a specific thickness is passed through, producing a specific amount of coating.    e) When the entire volume of solution of the bubble has been consumed (or before, if having a more regular process is desired), it is necessary to restart the process.
Furthermore, it must be highlighted that, while the internal volume of the casing increases in quadratic proportion with respect to the caliber, the inner surface only increases in linear proportion with respect to the caliber. The Surface/Volume ratio is therefore inversely proportional to the caliber, which means that it increases in a hyperbolic manner as the caliber drops.
For example, a volume V1 is necessary to coat the 100-meter inner surface of a Caliber 50 casing. That volume V1, introduced inside the Caliber 50 casing, involves bubble height (being conventionally considered as vertical, although the considerations would be similar for a bubble with any other orientation) of h1.
To coat the 100-meter inner surface of a Caliber 10 casing (with an amount of coating per surface similar to that of the preceding case of caliber 50), it is easy to demonstrate that the height of bubble must be 5×h1, i.e., 5 times greater than the preceding case.
The practical reasons dictate that the length of bubble must be limited since, for example, maintaining a casing with a column of many meters of liquid therein in movement would be unmanageable. The previous calculations show that low caliber casings need relatively greater bubble heights than the high calibers for producing a similar length of coating. Therefore, if desired, maintaining a maximum bubble height h1, both in the Caliber 50 casing and the Caliber 10 casing, will involve replacing the bubble 5 times more frequently in the Caliber 10 than in the Caliber 50, with all the subsequent processes (cutting, filling, slicing . . . ) it entails. This adds unacceptable operation costs the smaller the caliber is (and, therefore, generally, its market price), meaning that high cling casings below Caliber 36 are not commercially found. Therefore, while the “bubble” method is widely used in high caliber fibrous casings (reinforced cellulose casings), its application to low calibers is virtually nil (“low calibers” being understood as all those with a diameter less than 36 mm).
Therefore, there is a need in the state of the art to obtain small caliber casings with high cling characteristics to meat emulsion in an economical manner.
An alternative to the inner or outer resin coating in fibrous cellulose casings has been the direct incorporation of the resin into the viscose solution before extrusion in the corresponding coagulant baths. The resin solution is injected into the viscose circuit (US 2001/0045236 A1). Later on, during the casing drying process, the high temperatures of the dryer activate resin crosslinking.
The meat emulsion cling effect occurs mainly between said meat emulsion and the inner surface of the casing. In the case of reinforced cellulose casings in which a fibrous substrate is covered with viscose on their outer and/or inner face, the addition of resin to the viscose can be limited to the viscose used for coating the inner surface of the casing (U.S. Pat. Nos. 2,105,273, 6,395,356) which involves an optimum utilization of the resin. However, in the case of non-reinforced cellulose casings generally intended for much lower calibers than the fibrous ones, viscose tends to make up the entire thickness of the cellulose casing. The addition of the resin to the viscose will finally distribute the resin throughout the thickness of the casing and not only on the inner surface which is where it would be interested to obtain the desired meat emulsion cling effect. This means that the added amount of resin is much greater than that necessary for merely obtaining the coating in the inner layer, which involves extra expenses. Furthermore, the presence of resin in the thickness of the casing can have additional negative effects on the casing, for example, mechanical resistance variation undesirably modifying the end physical properties of the film.
Therefore, there is a need in the state of the art to develop alternative, economical and efficient techniques for obtaining casings with a high degree of meat cling, in particular casings of low caliber, for the purpose of overcoming the difficulties and drawbacks derived from the current bubble and viscose techniques commonly used for applying additives, providing the casing meat cling effect but without modifying the rest of the process leading to the manufacture of finish casing for the purpose of not introducing technological risks nor new elements of cost.
Finish casing or tube manufacture is a continuous process that finishes with winding same. The finish and inflated cellulose tube continuously exiting the dryer, is collapased by means of tamping rollers, thus evacuating air from its interior. A flattened tube in the form of a continuous flat belt is thus obtained, the tube is wound on a plastic or cardboard mandrel forming reels, accumulating a predetermined length of casing, until the reel acquires dimensions suitable for subsequent handling. The casing continuity is interrupted when the reel is separated from the process, being replaced with a new mandrel on which the winding of the next reel will continue.
The reels become a stock awaiting its access to a subsequent off-line process for converting the flat casing flat into sticks of shirred casing which is also “casing shirring”.
During the shirring process, the flat casing is first restored to its tubular shape to be longitudinally jacketed on a straight sleeve, along which it slides at great speed with the aid of a series of drive rollers, while it is sprayed with an aqueous dispersion or aqueous emulsion made up of one or several ingredients acting primarily as lubricant and plasticizer, as is well known in the art.
The rollers press on the outer wall of the casing while the inner face thereof rests on the polished metal sleeve. The disposition and geometry of the rollers creates a drive ring around the casing. When the rollers rotate, they drag the casing in the direction of rotation and in the direction of the axis of the sleeve (although the axis of rotation of the rollers is not exactly perpendicular to that of the casing-sleeve assembly). The simultaneous rotation of the rollers on the outer face of the casing creates enough driving force both for unwinding and dragging the casing to the inlet thereof, and for folding and compressing it at the same time against a braking device at the outlet thereof. Therefore it is possible to accumulate quite a few meters of casing in the shape of a straight and rigid folded tube (due to the heavy compaction of the folds therebetween) which has several centimeters of length and which is known as a stick in the field.
The additives sprayed on the cellulose casing during shirring have two main purposes: a) on one hand to lubricated the contact interphase between the inner face of the casing and the surface of the sleeve so that the sliding of the casing on same occurs with minimum friction; and b) on the other hand it has the purpose of preparing the casing to prevent any damage during folding and compaction. The additives added for this purpose in the shirring process can include, for example, plasticizer substances, such as glycerol, propylene glycol or other polyols, which also perform the function of delaying water intake by the cellulose casing given its high hygroscopicity (U.S. Pat. Nos. 3,898,348; 3,981,046).
Subsequently these additives can be combined with other additives the functionality of which is different. They can, for example, be combined with flavoring and coloring substances which are transferred to the meat, such as liquid smoke (CA 1325131), or such as a bixin colorant composition, as disclosed in patent ES2076904 A1 which also combine various water or alcohol soluble film-forming agents or mixtures of both such as cellulose esters, zein, casein, dextrins or starch derivatives or Shellac. The shirring solution has also occasionally included an additive facilitating the subsequent peeling of the casing (e.g., carboxymethyl-cellulose). It can also include a cellulose enzyme in order to remove the casing in skinless sausages (EP 1101406).
The additive or additive composition is generally sprayed on at the start of the shirring process by means of a nozzle located at the end of the sleeve penetrating and inflating the cellulose tube coming from the reel. The friction between the casing and the sleeve is thus reduced from the first moment of contact.
Based on the needs of the state of the art, the inventor of the present application has developed a composition for addition during the pre-existing shirring step, capable of conferring the casing with a high capacity to cling to the meat paste or product stuffed therein on its own.
Said composition comprises at least one heat curable polycationic resinous component, a polyolic component and water.
The moment of converting the smooth casing into a shirred casing is the most suitable casing production step for the coating, since in said process the continuous smooth casing is segmented and impregnated with various previously mentioned functional liquid compositions. However, for a heat curable resin this involves the drawback that there are no subsequent steps after shirring in which the heat necessary for curing of resin is applied, and in the case of having to add them, the starting economic principle would again be violated.
However, the experiments carried out by the author of the present invention has surprisingly and expectedly allowed obtaining a result where the resin, incorporated in the casing together with the rest of shirring additives, and without the need of heat curing, is capable of anchoring to the casing, thus overcoming the preconceptions established in this respect in the state of the art, since it has never occurred to the person skilled in the art to add an additive to a shirring composition which according to the existing knowledge can only be anchored to the casing by heat curing, since it would have run the risk of the folds sticking together making the subsequent casing extension impossible.
The casings impregnated with said shirring composition, in the absence of heat curing, cling, once stuffed, excellently to the surface of the meat mass that they contain and have an excellent performance in terms of the cooking and/or drying processes to which they are subjected, in turn assuring food safety.
The application of coating composition during shirring, making up a pre-existing part of the process, configures a qualitative technical advantage since it prevents the need of using other conventional methods such as the bubble or viscose method which are much more expensive and have the previously mentioned drawbacks.
Furthermore, another surprising fact derived from using this composition is that, despite the anchoring of the resin on the casing, the latter is not stuck to itself in the folds of the stick, as could happen after an inherent heat curing process of the resin such as that used in the previous technique as a result of the bubble method. In contrast, the sticks unfold perfectly during the stuffing process without causing any casing defect.
Finally, another important advantage derived from using the composition of the present invention is that the casings treated with the composition of the invention surprisingly have a perfect performance under unnatural processing conditions in their application on certain meat products stuffed in low calibers, which allows competition where natural casings of animal intestines and collagen-based casings are the only alternative to date.
This unexpected fact entails a great competitive advantage, since on one hand, the composition and method of the invention allows economically dealing with a greater number of calibers (especially low calibers) for those applications in which the meat casing cling is essential, and on the other hand, the resulting casings allow shortening some processing cycles of the stuffed products for which they may be intended, although these cycles are more aggressive, thus increasing the product profitability.